Is it possible to lose weight while on sequel?

Sure: Sure, it just take a little extra motivation.

Seroquel (quetiapine): I assume you meant seroquel (quetiapine) in your question. Seroquel (quetiapine) is known to contribute to weight gain. Nonetheless, it is a challenge but doable one. You will need to develop a healthy eating routine - avoid eating in the evening and at night. Also, watch what you're eating - avoid fast food, high sugary beverages. Increase veggies in your diet. Also, start regular exercise routine (cardio exercises).

You gain weight but: No normally you gain weight but you can minimize weight gain by cutting total calries and exercise, but it is very hard to loose weight while on seroquel having said that some people are able to loose weight by strict diet and exercise program and those are exceptions.